This invention relates to the control of maneuvering vehicles that operate in space and specifically relates to new and improved thrusters for such devices.
A space maneuvering vehicle is a specialized spacecraft, sometimes referred to as an orbit maneuvering vehicle (OMV), with propulsion capacity that is capable of retrieving other spacecraft, for servicing by a space shuttle orbiter or space station in low earth orbit, of placement of spacecraft into low earth orbits but at altitudes higher than the space shuttle orbiter is capable of reaching, and of docking of spacecraft in order to accomplish servicing tasks; all by remote control or through fully automated techniques.
To accomplish this, maneuvers in close proximity to spacecraft, including closing maneuvers and docking, the vehicle will be controlled by low level thrusters operating in conjunction with the vehicle's guidance and navigation system, under control of an operator situated at a ground based or space based control situation. For full control (6.degree. of freedom) a total of 24 thrusters are required located on the vehicle in the geometry approximately as depicted in FIG. 1; FIG. 1 being simply a parallelpiped representing the vehicle with groups of three thrusters, 12 fanning out from the eight corners of the vehicle.
However, there are complicating factors that can cause the requirement for thrusters to go up by a factor of three, to a possible total of 72.
First, for remote control of the maneuvering vehicle by a shuttle or earth-stationed operator, ie., manual control, a high level of thrust is desired in order that maneuvers can be accomplished in reasonable periods of time. This thrust level may be, for example 15 lbs per thruster. Second, however, when the maneuvering vehicle operates autonomously, ie, automatically, significant fuel savings can be effected if the control thrusters operate at a lower level, for example, 5 lbs of thrust per thruster. Normally, automated operations can take longer using less to accomplish than those that are under manual control. The importance of saving fuel is recognized due to the high cost of transportation to earth orbit; on the order of $1000 per pound. So propellant conservation is the resultant benefit from operating at a lower thrust level.
Lastly, when a maneuvering vehicle operates in close proximity to a spacecraft, the exhaust plume from the control thrusters is a source of contamination or possible damage to sensitive parts or to surfaces. It is therefore desirable to use an inert gas for thrusting when in close proximity to spacecraft.
So for these three possible modes of operation of a teleoperator, the following requirement arises for control thrusters:
______________________________________ Thrust Level No. Req. ______________________________________ Mode 1- Manual remote control 15 lbs 24 maneuvering vehicle Mode 2- Automated control 5 lbs 24 maneuvering vehicle Mode 3- Close proximity 1 lb.sup. 24 ______________________________________
Therefore, an object of this invention is to eliminate the need for a large number of control thrusters on a maneuvering vehicle yet maintain the performance capability thereof. More specifically, it is an object of this invention to reduce the requirement of control thrusters on a maneuvering vehicle from a possible 72 to a total of 24.
Still another object of this invention is to provide control thrusters for the vehicle which are easily removable from the vehicle and replaceable, to make the vehicle easily maintainable.